What is the consensus - during an interview, do you keep your suit jacket on or off?
What is the impression it gives if the suit jacket is taken off during the interview?
I will assume that you've determined already that a suit jacket is appropriate for the type of interview in which you find yourself.
The only times I ever remove my jacket during an interview is if it is insanely hot and I expect to be in there more than 15 minutes longer than I've already been there. I can suffer through just about anything for 15 minutes.
There are some exceptions I would make though:
Remember though, 1 overrides just about everything.
Also, realistically it probably doesn't affect your interview as long as you still look confident and professional without the jacket on, but I always opt for more formal, at least in the very first interview, and it's never served me wrong.
edit: As for the impression it gives, suit jackets say "I'm a professional" which is why I always leave mine on.
If you come in and see everyone's much less dressed up than you, you're probably safe to take it off. You could also say in this situation, "I'm getting a little warm. Do you mind if I take off my suit jacket?" If it's more formal, like everyone's obviously wearing business-casual or even more formal, it's probably safer to leave it on. I think a good rule of thumb is at least one step more formal than the interviewers. I might make an exception though if you're overwhelmingly uncomfortable in the suit jacket. You won't make a good impression if you choose to keep it on, and end up being really uncomfortable as a result.
I keep it on unless I think there are some situations where it is appropriate to take it off:
Otherwise, there's a reason you wore it to the interview in the first place, so be safe and keep it on.
Assuming the interview and employment offered is in an office setting, I wouldn't ever take my jacket off. In an interview it would show the interviewer that I was uncomfortable wearing one. Also, in today's very competitive world where we're not with the same employer for our entire career I'd suggest always having the jacket on.
I do everyday regardless of season because I think my professional brand image is important. You really never know who you'll meet at work, on your way to or from work or anyplace you go on company time. You don't want to be seen scrambling to put on your jacket or be seen looking uncomfortable introducing yourself to someone who just popped by while your jacket is on your chair instead of on you.
If you're a contractor with the business or a consultant who's working alongside employees but isn't one themselves I would definitely never be seen without my jacket on. Otherwise, it's more important to fit in with the boss than coworkers. Perhaps paying more attention to how attire is worn will promote you faster because you fit the look of someone who can be in a leadership position.
Either way, if you're like me and prefer to just keep your jacket on all throughout the day that should be perfectly fine. Just be consistent from day 1 of your interaction with people at the company and people will accept you for who you are. My rule of thumb is that there's no problem with looking too classy and there's no such thing as overdressed in an office setting. You want to consistently show, without saying a word about it, that there's a minimum standard you always wish to stay very high above regardless of employer.
In short, always tailor your suits to fit and have an investment in lighter weight suits for spring and summer. That way you don't get hot.